| 摘要 |
748,104. Reinforced concrete; floors; roofs; girders. PRE-STRESSED CONCRETE CO., Ltd., ISAAC, G., and LOWE, J. N. Dec. 2, 1954 [Nov. 17, 1953], No. 31870/53. Class 20(4). In addition to pre-stressing cables concrete members are reinforced by steel &c. ducts which accommodate the cables and by mesh formwork as of metal, expanded metal, plastic or strong textile material upon which the concrete is laid. For a floor or flat roof, mesh 1 is laid on scaffolding and ducts 2 of inverted U- shape and stirrups 6 are placed in position and wired or welded to the mesh, concrete 1¢ in. thick then being laid and when cured placed in compression by cables which are kept in tension within the ducts by means of washers and cones 8. Light cavity formers 9 are located between the stirrups and concrete 10. The concrete protrudes somewhat through the mesh and forms a rough keying surface for a subsequent rendering. The ducts 2 may be dispensed with by bending the mesh to form longitudinal ridges to accommodate the cables. In a modification separate planks are cast on a level bed, the mesh being cut to the length and breadth required, two ducts and an intermediate reinforcement bar being laid on it. After the planks are cured and the cables tensioned the planks are inverted and grout is poured into the ducts. At the site the planks are supported on scaffolding at 4 ft. intervals along their length, formers are laid clear of the gaps between the planks and concrete and a finishing screed surmounted by a surfacing material are applied. A further construction embodies an arched roof built up of similar planks which are arched to the required shape as by a tie member. A relatively deep layer of lightweight concrete may replace the structural concrete and formers.
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